This invention relates to a suppressant of corneal subepithelial clouding that contains .gamma.-interferon as an active ingredient. More particularly, the invention relates to a suppressant of corneal subepithelial clouding which develops after superficial keratectomy with an excimer laser, as well as a method of suppressing the corneal subepithelial clouding.
Eye glasses and contact lenses are devices that are capable of very safe and reliable correction of myopia, hyperopia and astigmatism due to corneal ametropia. However, they suffer the serious disadvantage of the need to be worn by the user. In certain cases, it is impossible to correct errors in refraction by means of eye glasses and contact lenses.
Since S. L. Trokel et al. first proposed the ophthalmologic application of an excimer laser in 1983 (Am. J. Ophthalmol., 96: 710-715, 1983), adaptations of the excimer laser to clinical ophthalmology have been the subject of many researchers. The recent years have seen progresses in clinical studies on the use of excimer lasers in the correction of myopia and astigmatism and in the treatment of corneal superficial clouding. Superficial keratectomy (SK) using an excimer laser was first reported by O. Sordaravic et al. in 1985. Use of an excimer laser in the correction of in myopic refractive errors was tried by M. B. McDonald in 1988. Since the result was incomparable to the conventional therapies, the new approach was incorporated in a therapeutic experiment under the regulatory control of the FDA. A clinical study of Phase III started in 1991 and the monitoring of the results continues. In Europe, Seiler and his coworkers have been carrying out clinical studies since 1988. A full-fledged clinical therapeutic experiment started in 1993 in Japan (Yoshiaki Hara, Practical Ophthalmology, 178-181, 1993; Shigeru Kinoshita, Atarashii Ganka (New Aspects of Ophthalmology), 10(2): 221-224, 1993; Masakazu Yamada, Ganka (Ophthalmology), 35:347, 1993).
Superficial keratectomy using an excimer laser covers various applications of an excimer laser to the cornea and it may be classified as follows in accordance with the operative technique used (Keizo Takahashi, Practical Ophthalmology, 187-193, 1993 and Shigeru Kinoshita, Atarashii Ganka (New Aspects of Ophthalmology), 10(2): 221-224, 1993):
(1) Phototherapeutic keratectomy (PTK) which involves the ablation of corneal superficial clouding (this technique has good adaptation to cases of subepithelial clouding such as granular corneal dystrophy, lattice corneal dystrophy, gelatinous globular corneal dystrophy and zonal corneal dystrophy);
(2) Photorefractive keratectomy (PRK) which involves the correction of myopia by reducing the corneal refractive power; and
(3) Astigmatic T-excision and photoastigmatic keratectomy (PAK) which are directed to the correction of corneal astigmatism.
While the utility of excimer lasers in the ophthalmologic area is being established, several problems that need solution have been pointed out. The biggest problem is corneal subepithelial clouding (shallow, diffused retiform clouding just below the epithelium) that develops at the site of laser application and which can be result in lower vision. This clouding peaks in 1-2 months after the operation and it has been postulated, but not established, that this is caused by in collagen synthesis which takes part in the healing of wounds or certain changes mucopolysaccharides. Attempts are being made to suppress the subepithelial clouding of the cornea by applying steroids to the eye. However, opinions are divided as regards the use of steroids and, considering negative points such as inadequacy of their efficacy and possible side effects, steroids are not a complete solution to the problem. Unless this problem is solved, one cannot say that all visual functions are restored and, hence, the problem that prevents clinical applications of an excimer laser to the ophthalmologic area persists and needs an effective solution.